Q-switching device for glass lasers

ABSTRACT

An improved Q-switched neodymium laser in which uranium as UO2 2 and a uranium oxidizing agent such as cerium in a host body such as glass serve as either an external or an internal Q-switching device for the laser.

United States Patent Greenberg Feb. 11, 1975 Q-SWITCHING DEVICE FORGLASS 3,457,183 7/1969 Lee et a1. 252/301.4 F LASERS 3,471,409 10/1969Lee etal 106/52X 3,640,890 2/1972 Lee et a1. 1. 331/945 E X [75]Inventor: Charles B. Greenberg, Turtle Creek,

Pa. OTHER PUBLICATIONS 1 Assigneei PPG-hldllSlliBS, -9 Pittsburgh, Pa.Melamed et 111., Laser Action in Uranyl-Sensitized Nd-Doped Glass,"Applied Physics Letters, Vol. 6, [22] Flled. Aug. 21,1970 NO. 3' 1965,pp 454- [21] Appl. No: 65,894

Related U.S. Application Data Primary Examiner-Harvey E. Behrend [63]Continuation-impart of Ser. No. 673,614, Oct. 9, Assistant Schafer 1967,abandoned. Attorney, Agent, or Firm-Dennis G. Millman; William J. Uhl[52] U.S. Cl. 252/301.1 L, 106/52, 252/300, 252 301.1 R, 252 301.4 R,252 301.4 F,

33/1/94 5 E [57] ABSTRACT [51] 'f CI H015 3/00, Cogk 1/301 C091 1/10 Animproved Q-switched neodymium laser in which [58] Field of Search252/301.1 R, 301.1 L, 300, uranium as +2 and a uranium oxidizing agentSuch 252/3014 3014 F; 106/52; 331/945 E as cerium in a host body such asglass serve as either an external or an internal Q-switching device forthe [56] References Cited lasen UNITED STATES PATENTS 3,417,345 12/1968Cabezaset a1. 331/94.5 E 4 1 Drawmg CONTROL c 19 EUUFNTH! E 1 i975INVENTOR CHARLES E. GfiEf/VBERG ATTORNEYS Q-SWITCHING DEVICE FOR GLASSLASERS CROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of copending application Ser. NO. 673,614, filedOct. 9, 1967, now abandoned.

The present invention relates to lasers and it has particular relationto a Q-swi'tchin'g device for glass lasers.

A laser, by definition, is a device that amplifies light by stimulatedemission of radiation and is specifically adapted to producehigh-intensity, coherent, mono= chromatic light in a narrow beam. Light,in this definition, is not limited to radiation in the visible region ofthe spectrum. Lasers in the form of glass or crystalline rods are wellknown. In such form the glass or crystal acts as a host for an elementwhich radiates energy at particular wavelengths at a greatly amplifiedlevel (above and beyond that of fluorescence due to the manner in whicha laser acts.

The action of a glass laser is described in several publications. Theseinclude a book entitled Introduction to Laser Physics written by Bela A.Lengyel and published in 1966 by John Wiley and Sons, lnc. of New York,New York Library of Congress, Catalog Card No. 65-27659, and an articleentitled Glass Lasers" by Dr. E. Snitzer starting at page 1487, Vol. 5,No. 10, Applied Optics, Oct. 1966.

A number of elements have been found to lase in glass. These include Nd,Yb and H Neodymium is the most important of these because it can beoperated efficiently at room temperature as a four-level laser. A numberof glass and crystal compositions have been developed to act as hostsfor lasing'elements, particularly neodymium. These compositions are setforth in the above references as well as in the following patents:

U.S. 3,225,306 (CaWO,)

U.S. 3,250,72l (Phosphate) US. 3,252,103 (A1 0 U.S. 3,254,031 (Borate)U.S. 3,257,625 (Molybdate) U.S. 3,258,715 (CaF U.S. 3,220,290(Lime-soda-silica) British 1,015,057 (Barium Crown) For purpose ofunderstanding the present invention, a brief description of laser actionis provided. A more detailed explanation is set forth in the book andarticle mentioned above.

Light is produced in a laser by photonic emission from the active atomsof a body composed of a socalled laser material. This emission occursincident to the transition of the atoms from an excited, high energylevel to a lower energy level. Accordingly, laser operation essentiallyinvolves exciting active atoms in the laser body to a high energy level,and inducing the emissive transition of the excited atoms in a mannercontrolled to utilize the light thereby emitted to provide the desiredlaser output pulse. The nature and number of inter-level transitionswhich must be effected in a complete atomic cycle or laser operation aredependent on the properties of the particular laser material used.

One conventional form of laser structure includes a rod-shaped bodycomposed of a suitable solid laser material, such as syntheticcrystalline ruby (3-level) or heodymium glass (4'-level), surroundedconcentrically by a helical gaseous discharge tube (commonly called aflash tube), which is adapted to emit a pulse of light specificallyincluding light in the wavelengths of absorption bands of the lasermaterial. When the flash tube is actuated, the light pulse enters thetransmissive laser body, pumping the body with energy of suchwavelength. This pumping excites active atoms in the laser body to shiftfrom an initial ground level in a series of inter-level transitions,typically involving a first energy-absorptive transition to a veryunstable high energy level and an immediately subsequent spontaneous andnon-radiative transition from this unstable level to a somewhat morestable high energy level (intermediate in energy between theaforementioned ground and unstable levels) and from which fluorescenttransition occurs. The pumping pulse provides the excitation step inlaser operation creating a very large population of active atoms at thehigh energy, fluorescent level in the laser body. The system can lasewhen the population of active atoms at the fluorescent level exceedsthat of the terminal level. This is population inversion.

For effecting induced light-emissive transition from this high energylevel to complete the atomic cycle of laser operation, the laser body ofthe structure is disposed coaxially within a resonant cavity definedbetween opposed internally reflective cavity ends. A portion of thelight emitted by the spontaneously emitting atoms passes through theresonant cavity to the ends thereof, and is thence reflected back andforth through the cavity between the reflective cavity ends, passing andrepassing in multiple bidirectional reflections. This bidirectionalreflected light induces other atoms at the fluorescent level to undergoemissive transition to the terminal level, producing more light in thecavity to induce still further emissive transitions from the fluorescentlevel population. ln such fashion, a rising pulse of bidirectionallyreflected light quickly develops within the cavity, reaching aquantitatively large value as the induced emissive transition of atomsfrom the fluorescent level population becomes massive. Light of highintensity is accordingly created in the form of a pulse as a result ofthe pumping.

To permit emission of a portion of the large bidirectionally reflectedlight pulse from the laser cavity, one reflective end of the cavity ismade partially transmissive. The fraction of the bidirectionallyreflected light escaping therethrough constitutes the laser outputpulse.

In laser operation of the foregoing character, the energy-pumping pulseis of finite duration. Excitation of atoms to the fluorescent energylevel occurs throughout this finite pumping period. However, with alaser cavity maintained internally reflective at both ends, lightemitted by spontaneous emission from atoms in the fluorescent levelpopulation begins to reflect back and forth in the cavity and in sodoing induces emissive transitions of other fluorescent level atoms insignificant number and initiates the laser output pulse substantiallybefore the end of the pumping period. During the pumping period, theeffect of the pumping pulse in augmenting the fluorescent levelpopulation is offset by the depletion of the latter population due tolasing transitions; The net result is that the number of atoms at thefluorescent level diminishes instead of continuing to increase to aneven greater population inversion as would otherwise be possible in theabsence of induced emission.

It can therefore be seen that the same pumping pulse could create asignificantly larger maximum fluorescent level population in the laserbody if the transitioninducing state created by multiple lightreflections could be retarded until a later time in the pumping period.Such delay of the latter state would be desirable, because the magnitudeof the peak power attained by the laser output pulse is directly relatedto the magnitude of this maximum fluorescent level population, and it isoften regarded as very desirable to obtain as large a peak power outputas possible for optimum laser utility. In other words, the prevention ofpremature bidirectional light reflections, thereby allowing developmentof a larger fluorescent level population, would enable attainment of apeak power output advantageously greater than that produced with thenon-retarded laser operation described above.

it has been found that the multiple bidirectional reflections ofspontaneously emitted light can be delayed in the desired manner by atechnique hereinafter referred to as Q-switching. This technique is alsosometimes referred to as Q-spoiling or giant pulse creation. The Q, orquality factor, of the laser resonant cavity is proportional to the.ratio of wave energy storage to wave energy dissipation per wave cycletherein. When one end of the cavity-providing structure isnonreflective, the resultant structure is said to be in a low Qcondition because light emitted by spontaneous transition of fluorescentlevel atoms in the laser body cannot refleet back and forth in multiplereflections through the structure, but is instead dissipated at thenonreflective end after at most two passes through the structure. inthis condition, bidirectional light reflections cannot build up toinduce emissive transition of high level atoms in significant number.

The Q-switching operation involves maintaining the cavity-providingstructure in a low Q condition during that portion of the pumping pulserequired for the fluorescent level population to reach a high value(which is substantially larger than the population of atoms attained inthe non Q-switched operation). Then, when a high population inversion isachieved, the previously nonreflective end of the cavity structure iscaused to become reflective, thereby switching the structure to aso-called-high Q condition. Multiple bidirectional reflection of lightproduced by spontaneous emission in the laser body begins upon suchswitching, and quickly rises by induced emission from atoms in the verylarge fluorescent level population previously established. The resultantlaser output pulse is much faster in rise time, and very desirablyhigher in peak power, than the pulse produced in the non-Q-switchedlaser operation.

An example of apparatus which includes a Q- switching device is shown inU.S. Pat. No. 3,281,712. In this apparatus, the Q-switching isaccomplished mechanically by means of a shutter composed of a planeopaque member having a surface of minimal reflectivity and an apertureor slit. The shutter is disposed in the laser apparatus between thelaser and one reflective surface so as to prevent bidirectionalreflection of light therethrough except when the aperture in the shutteris in line with the light transmitted from the laser.

Another example of a Q-switching device is the use of a glass in placeof the shutter described in U.S. Pat. No 3,281,712. The glass ischaracterized by having the property of saturable absorption at thelasing wave length. Q-switching can also be accomplished internally byincorporating an element in the laser glass which causes selfQ-switching. This is described by N. T. Melamed, C. Hirayama and P. W.French in an article published in Applied Physics Letters, Vol. 6,Number 3, dated Feb. 1, 1965, page 43.

The Q-switching phenomenon is generally described as a consequence ofsaturable absorption at the lasing wave length by some ionic speciesother than the active lasing ion. The incorporation of uranium in aneodymium glass permits the neodymium glass to self Q-switch. Thisoccurs because of excited state saturable absorption in the U0 energyscheme. The U0 species of uranium is of special interest because it alsoserves as a sensitizer (energy transfer) in Nd glasses and in Nd plus Ybplus Yb glasses. The function of the uranium as a sensitizer is toabsorb energy from the energizing source and transfer it to theneodymium after a suitable build-up. Theneodymium is said to besensitized by the uranium in this case.

The present invention is concerned with an improvement in a Q-switchedlaser employing a lasing element such as neodymium in combination withuranium. The uranium can serve as an external Q-switcher by being in aglass separate from the neodymium glass or as an internal Q-switcher bybeing incorporated in the neodymium glass. In accordance with thepresent invention, it has been found that the valence state of theuranium is critical as far as the efficiency of its sensitizing andQ-swiching functions are concerned.

Uranium is present in a glass in a plurality of valence states, namelyU, U and U0 (uranyl). it has been found that the ground state absorptionof uranium at 1.06 microns wavelength is influenced by the valence stateof the uranium. This is important since it is the radiation of neodymiumat 1.06 microns which is the las-' ing radiation. Catastrophic groundstate absorption losses at 1.06 microns wavelength occur in a uraniumglass melted in the absence of a strong redox oxidizing agent. Theseground state absorption losses are less as more of the uranium ispresent in its fully oxidized state, namely U0 In accordance with thepresent invention, a uranium glass is provided in which the proportionof the uranium which is present in the U0 state is greatly enhanced.This is accomplished by incorporating in the glass an element whichserves to establish and/or maintain the uranium during the melting ofthe glass in its most fully oxidized state, namely U0 One means ofaccomplishing this is to include cerium in the glass in an amount whichis sufficient to insure that 91 percent of the uranium is in the desiredvalence state in the glass after melting and cooling to roomtemperature. The glass is annealed during cooling to serve theparticular laser use according to conventional practice.

The invention in its embodiment as an external Q- switching device isshown diagrammatically in the accompanying drawing. Referring to thedrawing, a cylindrically shaped laser rod 10 of neodymium-containingglass is shown. The rod has opposed, plane, parallel end facesperpendicular to its long axis. One end face of the rod 10 is silveredas indicated at 11, to make it internally reflective. The other end issubstantially nonreflective.

A source of pumping light energy for the rod is provided by a helicalflash tube 13 disposed to surround the rod concentrically forsubstantially the entire length of the rod, but in spaced relation tothe rod. This flash tube functions on the gaseous discharge principle,and is specifically adapted to emit pulses of light including light inthe wavelengths of the absorption bands of the laser material. 1t ispowered from an appropriate power source 14, of conventional design andincluding a high-voltage source of electric current and capacitors forenergy storage, which are connected through leads 15, 16 to the oppositeend electrodes of the tube. Typically, such a power source for a lasersystem flash tube may be adapted to provide an input to the flash tubeof about 1,000 joules, at a voltage input of about 1 kilovolt.

The pulse producing discharge in the flash tube is initiated by means ofa trigger circuit 17, shown as encircling the turns of the helical flashtube in proximity thereto and powered from a suitable controlinstrumentality indicated at 18. The character and arrangement of theseelements is such that with sufficient charge energy developed in thepower source 14, an electrical pulse passed through the trigger circuit17 by the control instrumentality 18 will cause such pu1se-producingdischarge in the flash tube, and thus produce an input of pumping lightenergy to the laser rod at a time controlled by the instrumentality 18.

The laser rod and flash tube 13 are surrounded concentrically by anopen-ended hollow cylindrical member 19 having a reflective innersurface, to concentrate the pumping light emitted by the flash tube onthe rod 10.

An external resonator 20 is located in axially spaced relation to therod at the end opposite from the end of the rod containing the silveredsurface 11. Intermediate to the rod 10 and the resonator 20 there islocated an external Q-switching device 21. The device 21 is positionedwithin the reflective member 19 and power source 14 in order to beexcited by the energy from the power source 14. Alternatively, thedevice can be pumped by a separate power source (not shown) if thedevice is located external to the pumping source 14. The device 21 iscomposed of a uranium-containing glass and has plane, parallel, polishedsurfaces which are perpendicular to the axis of the rod. 1t functions asa Q-switching device in this set-up by preventing multiple reflection ofthe emitted photons along the axial path of the laser rod. It preventsthis reflection by absorbing substantially all of the photons whichwould be reflected by the resonator 20. This absorption continues untilthe glass is saturated at the lasing wavelength. Thereafter, thephotons, at 1.06 microns, pass through the glass and multiplereflections can occur, thereby permitting high energy lasing.

As example of glass that can be used in accordance with the presentinvention as an external Q-switching device is described in thefollowing example.

EXAMPLE 1 The following batch ingredients are utilized:

The sand is leached in 4N HCl plus 4 percent by weight of 52 percent byweight HF to lower the Fe O content from about 50 parts per million toabout 4 to 5 parts per million based upon the weight of the sand. Thistreatment is carried out over a period of about 1 week. The other batchingredients are chosen to minimize the iron content of the batch sinceiron adversely affects the ability of the laser glass: to operateproperly. Thus reagent grade batch materials are selected when everpossible. The batch materials are mixed and handled in iron-freecontainers to prevent the possibility of iron contamination. The glassbatch materials are selected from those which when melted and cooledform a glass which is suitable for laser applications.

The batch materials are heated in a platinumrhodium (-20) crucible in anelectric furnace at 2,600F. under oxidizing atmospheric conditions. Themolten glass is poured into a stainless steel mold, removed from themold upon solidification and cooled gradually from 930F. to roomtemperature over a period of about 16 hours. The glass has a calculatedcom position as follows:

The uranium is calculated as though all of it is pres ent as U0 however,some of the uranium is not present in this state as will be describedhereinafter.

The valence states of the uranium in the glass are determined bycomparing the absorption spectra of this glass and a glass produced inthe same manner, but omitting cerium. The molar absorption coefficientis determined to be 32 square centimeters per mole at 0.41 micron whichis the major UOf absorption band. From this and Beers law theconcentration of uranium which is actually present as U0 in theceriumcontaining glass is 91 percent of the total uranium content. It isonly 63 percent in the cerium-free analog glass.

The ground state absorption coefficient of the glass at 1.06 microns iscritical when the glass is to be used as an external Q-switcher for aneodymium glass laser. In this regard, it is the absorption by reducedstates of uranium such as U and U states that is important. The Llabsorption band which is centered at 0.92 micron wavelength has a longwavelength tail which imparts an absorption loss at 1.06 microns.Similarly U has a ground state absorption band centered at about 1micron. The ground state absorption coefflcient of the cerium-containingglass is 0.003 per centimeter and for the same glass without the ceriumis 0.035 per centimeter. Thus the cerium-containing glass acts as abetter window for permitting passage of the photons after the saturableabsorption state is reached as heretofore described in this Example 1.

EXAMPLE 11 The best mode of carrying out the invention involves aninternal Q-switching device. In this mode, an increased amount of theuranium is caused to be present in its fully oxidized state (UO in aneodymiumcontaining glass by including an oxidizing agent such as ceriumin the glass. The following batch ingredients are tuned: tional means toform laser rods measuring A inch in di- Pans by we'ght ameter and 6inches in length. Sand) g2? A glass prepared as above is compared with aglass c 1310 made in the same manner, but without cerium. The ggi alzz25-2 10 static absorption loss at 1.06 microns for the cerium- M10acontaining glass is 0.003 per centimeter and for the glass withoutcerium is 0.0187 per centimeter. Charac- The sand is leached asdescribed in Example I. The teristics of these self Q-switched laserglasses atseveral 7 other batch ingredients are chosen to minimize theiron e'ner gy'i nputs using 85 and 99 percent confocal resonacontent ofthe batch, thus, reagent grade materials are tors and a rod size of Ainch diameter by 6 inches selected. The batch materials are mixed andhandled in length, are shown in the following Table I wherein glassiron-free containers to prevent the possibility of iron No. l is theglass containing cerium and glass No. 2 is contamination. the glasswithout cerium.

TABLE I Input Average Average Spiking Threshold Glass Energy Pulse WidthPeak Power Frequency Energy No. (Joules) (Nanoseconds) (Megawatt)(Kilohertz) (Joules) l 576 186 0.5 31 70.4 2 576 247 0.1 45 144 l 1089H9 L5 28 70.4 2 1089 145 0.4 30 144 The batch materials are char ed overa eriod of The results in Table 1 reveal im roved iants ike o g P 30 P gP P time mto a platmum-lined, refractory, 8-mch pot situeratlon, pulsewidth reduct1on of about 20 percent and ated in an electric meltingfurnace having an atmoan increase of peak power of about 300 percent to500 spheric temperature of 2,510F. Approximately 12 percent in glass No.l. The threshold energy input is pounds of batch are charged in thefollowing amounts lowered by about 50 percent in glass No. I. over thefollowing schedule at the given temperatures.

Time Amount (Minutes from Start) Temperature (F.) (Pounds) Start 25m. 6EXAMPLE 111 55 2550F. 2 80 2550F. 2 I25 2500F. l l55 2570F. l

v 0 230 Convent1onal neodymlum laser glasses contam The batch is thenstirred at 2 p means of a Sb O which serves as a fining agent andinhibits solarplatinum stirrer for about 3 hours, held at 5 1zat1on. Forthis reason, addmonal melts of the preovernight for about 16 hourswithout stirring, and then fer'red glass were made f Sb2o3 f and wlthstirred for about 4 hours at 2,750F. and for 2 A hours femlg amounts ofand oxldlzmg agms f while the interior temperature of the furnace isreduced Cludmg none) to determme the effect of havmg gradually to2,450F. All of the above is done while the mony m Fhese glasses- Theresults of tests of these furnace is in an oxidizing condition glasseswith respect to the important property of Thereafter the glass isremoved from the furnace and ground state absorption loss at 1.06microns are shown cast as a square slab approximately 14 X 14 inches bym Table l A inches in thickness. The glass is then cooled to roomtemperature, reheated to l,080F. and annealed slowly over a period of240 hours from l,080F. to

0 room temperature at a rate of about 2 to 10 F. per TABLE n hour.

The calculated and chemically analyzed composinons of the glass are asfollows: Nominal Doping (Percent by Weight) Absorption Parts by WeightGlass Per Ingredient Calculated Analyzed No. Nd O U0 Sb O CeO CentimeterSiO, 58.5 57.94 I 4 0.5 0 0.5 0.003 BnO 2l.7 21.25 2 4 0.5 l 0 0.0187K,0 14.92 15.14 3 4 0.5 1 0.5 0.0137 110," 0.48 0.75 4 4 0.5 1 0 0.01117(C0, 0.48 0.54 5 4 1.0 1 0.5 0.0193 Nap, 3.92 3.56 6 4 L0 1 0 0.026Other 0.72 7 4 L5 1 0.75 0.0252

| 00 mom 8 4 1.5 1 O 0.057

The uranium is calculated as though all of it is present as U0 however,some minor proportion of the uranium, preferably none, is not present inthis state.

The glass is then ground and polished by conven- From the results inTable II it can be seen that appar ently Sb O interferes with theoxidation of U to some extent, although significant reductions in groundstate absorption of 25 percent to 50 percent are still obtained.

The ground state absorption at l.06 microns in the laser glass isdirectly proportional to the uranium in the glass. There should besufficient cerium present to oxidize the uranium in the glass to the U0state to as great an extent as possible. For example, in Example I thepercentage or uranium present as U0 was increased from about 63 percentto 91 percent when cerium was added. This reduced the ground stateabsorption by an order of magnitude. Larger amounts of cerium arerequired as larger amounts of uranium are employed in order to obtainmaximum reduction in ground state absorption.

The amount of the essential ingredients can vary in percent by weightfrom O to 30 percent Nd O 0.01 to l5 percent U0 and 0.01 to 20 percentCeO based upon the weight of the glass. When the invention is employedas an external Q-switching device, there need be no neodymium in theglass. When the invention is employed as an internal Q-switching device,the glass can contain 0.01 to 30 percent by weight of neodymium oxide.

Although the invention has been described with respect to two specificglasses as the best modes contemplated by the inventor for carrying outthe invention, the practice of the invention is by no means limited tothese particular glasses. When the host glass is a barium crown glass,the glass may contain 20 to 70 percent SiO 5 to 30 percent BaO, 5 to 40percent K 0, 0 to 2 percent Sb O as well as 0.01 to percent U0 and 0.01to percent CeO as the essential ingredients. The host glass mayalternatively be glasses such as lime-sodasilica glass, high silicaborosilicate glass, germanate glass, flint glass, lead silicate glass,and certain organic glass-like plastic materials such as methylmethacrylate, acrylics, rigid vinyl chloride, glycerine and EPA. Theterm glass is intended to include in its broadest sense, both organicand inorganic rigid materials which are of a plastic-like nature havinga nonperiodic atom structure as distinguished from materials havingtheir atoms in an orderly periodic array.

The laser host body may be either glass or crystalline in nature. Theinvention applies to crystals doped with neodiumium such as thosereferenced above in the prior art. The invention also applies to glassand crystalline lasers wherein the active lasing element emits in thesame regions of the optical spectrum wherein the reduced states ofuranium have significant ground state absorption at the lasingwavelength. For example, the invention is applicable to ytterbium lasersand ruby lasers. The critical wavelength for ytterbium is 1.06 micronslike neodymium, whereas the critical wavelength for a ruby laser is 0.69micron. The reduced states of uranium absorb over a wide portion of thelaser spectrum.

Although the invention has been described with regard to specificdetails of certain preferred embodiments of the invention, it is notintended that such details be considered as limitations on the scope ofthe invention except insofar as included in the accompanying claims.

I claim: 1. A process for producing a self Q-switching device adaptedfor use in a laser comprising:

a. melting i. a mixture consisting essentially of glass batch materialswhich are substantially iron-free, and which when melted and cooled forma glass which is suitable for laser applications, ii. a uranium salt,and iii. cerium dioxide, and b. cooling said melt to form a solid glass,said uranium salt being present in said solid glass in an amountsufficient to provide a uranium salt being present in said solid glassin an amount sufficient to provide a uranium content, expressed as U0 of0.01 percent to 15 percent by weight, based on the weight of said solidglass and said cerium dioxide being present in an amount sufficient toconvert at least 91 percent of said uranium to a U0 valence state. 2.The process according to claim 1 in which said cerium dioxide is presentin an amount of 0.01 to 20 percent by weight.

3. A laser glass having substantially the following composition inpercent by weight:

SiO 2O B30 5 3O K 0 5 40 Sb O 0- 2 Uranium (expressed as U0 0.01 l5 ceo0.01 20 Nd o 0.01 30 with at least 91 percent ofthe uranium in the glasspresent in the U0 valence form.

4. A process for producing a self Q-switching device adapted for use ina laser comprising:

a. melting a mixture consisting essentially of i. glass batch materials,which are substantially iron-free which when melted and cooled form aglass selected from the class consisting of barium crown glass,lime-soda-silica glass, high silica borosilicate glass, germanate glass,flint glass, and lead silicate glass,

iii. cerium dioxide,

b. cooling said melt to form a solid glass, the UO NO 6H O being presentin an amount sufficient to provide a solid glass having a uraniumcontent expressed as U0 of 0.01 to 15 percent by weight based on theweight of said solid glass and said cerium dioxide being present in anamount of 0.01 to 20 percent by weight.

UNITED STATES PATENT GFFIQE CERTIFICATE or PATENT NO. 2 3,865,747

DATED 1 February 11, 1975 INVENTOWS) I Charles B. Greenberg It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 19, after "fluorescence" insert Column 1, line 30, after"Yb insert Er Column 1, line 46, "purpose" should be purposes-.

Column 1, line 62, "or" should be -of.

Column 2, line 34, after "light", insert -which augments thebidirectionally reflected light-..

Column 4, line 15, after Yb delete plus Yb Column 5, line 52, delete"As" and insert -An-.

Column 9, line 44, "atom" should be --atomic--.

Signed and sealed this 15th day of July 1975o (SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks UNITED STATES ATENT @FFEQE CERTIFICATE 1 term PATENT NO.3,865,747 DATED 1 February 11, 1975 mvrsmoms) Charles B. Greenberg It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below;

Column 1, line 19, after 'fluorescence" insert Column 1, line 30, afterYb insert Er Column 1, line 46, "purpose" should be --purposes--.,

Column 1, line 62, "or" should be --of--.

Column 2, line 34, after "light" insert ---which augments thebidirectionally reflected light -w Column 4, line 15, after "Yb delete'plus Yb Column 5, line 52, delete "As" and insert --An--.

Column 9, line 44, "atom should be --atomic--.

Signed and sealed this 15th day of July 1975@ (SEAL) Attest:

C MARSHALL DANN RUTH C. MASON Coissioner of Patents Attesting Officerand Trademarks

1. A PROCESS FOR PRODUCING A SELF Q-SWITCHING DEVICE ADAPTED FOR USE INA LASER COMPRISING: A. MELTING I. A MIXTURE CONSISTING ESSENTIALLY OFGLASS BATCH MATERIALS WHICH ARE SUBSTANTIALLY IRON-FREE, AND WHICH WHENMELTED AND COOLED FORM A GLASS WHICH IS SUITABLE FOR LASER APPLICATIONS,II. A URANIUM SALT, AND III. CERIUM DIOXIDE, AND B. COOLING SAID MELT TOFORM A SOLID GLASS, SAID URANIUM SALT BEING PRESENT IN SAID SOLID GLASSIN AN AMOUNT SUFFICIENT TO PROVIDE A URANIUM SALT BEING PRESENT IN SAIDSOLID GLASS IN AN AMOUNT SUFFICIENT TO PROVIDE A URANIUM CONTENT,EXPRESSED AS UO2+2, OF 0.01 PERCENT TO 15 PERCENT BY WEIGHT, BASED ONTHE WEIGHT OF SAID SOLID GLASS AND SAID CERIUM DIOXIDE BEING PRESENT INAN AMOUNT SUFFICIENT TO CONVERT AT LEAST 91 PERCENT OF SAID URANIUM TO AUO2+2 VALENCE STATE.
 2. The process according to claim 1 in which saidcerium dioxide is present in an amount of 0.01 to 20 percent by weight.3. A laser glass having substantially the following composition inpercent by weight:
 4. A process for producing a self Q-switching deviceadapted for use in a laser comprising: a. melting a mixture consistingessentially of i. glass batch materials, which are substantiallyiron-free which when melted and cooled form a glass selected from theclass consisting of barium crown glass, lime-soda-silica glass, highsilica borosilicate glass, germanate glass, flint glass, and leadsilicate glass, ii. UO2(NO3)2 . 6H2O iii. cerium dioxide, b. coolingsaid melt to form a solid glass, the UO2(NO3)2 . 6H2O being present inan amount sufficient to provide a solid glass having a uranium contentexpressed as UO2 2 of 0.01 to 15 percent by weight based on the weightof said solid glass and said cerium dioxide being present in an amountof 0.01 to 20 percent by weight.